SPPCM from C#

sppcm.cs

using System;
using System.IO.Ports;
using System.Threading;

namespace Sppcm
{
    internal class Program
    {
        private static SerialPort _serial;
        private static double _phase;
        private const double Frac = 440;
        private const double SamplingRate = 50000.0;
        
        const int SampleCount = 50;

        private static void SendBuffer()
        {
            var buffer = new byte[SampleCount * 5];

            for (var i = 0; i < SampleCount; i++)
            {
                var lch = Math.Sin(2.0 * Math.PI * Frac * _phase) * 0.5;
                var rch = Math.Sin(2.0 * Math.PI * Frac * _phase) * 0.5;
                _phase += 1.0 / SamplingRate;

                if (lch > +1.0) lch = +1.0;
                if (lch < -1.0) lch = -1.0;
                if (rch > +1.0) rch = +1.0;
                if (rch < -1.0) rch = -1.0;

                var lchShort = (short)Math.Round(lch * 32767);
                var rchShort = (short)Math.Round(rch * 32767);

                buffer[5 * i + 1] = (byte)(lchShort >> 8);
                buffer[5 * i + 2] = (byte)lchShort;
                buffer[5 * i + 3] = (byte)(rchShort >> 8);
                buffer[5 * i + 4] = (byte)rchShort;
            }

            if (_serial.IsOpen)
            {
                _serial.Write(buffer, 0, buffer.Length);
                _serial.BaseStream.Flush();
            }
        }

        private static void SendEmptyBuffer(int frameCount)
        {
            var buffer = new byte[frameCount * SampleCount * 5];
            _serial.Write(buffer, 0, buffer.Length);
            _serial.BaseStream.Flush();
        }

        private static void Main()
        {
            Thread.CurrentThread.Priority = ThreadPriority.Highest;
            using (_serial = new SerialPort("COM4", 3000000, Parity.None, 8, StopBits.One))
            {
                _serial.ReadBufferSize = 2;
                _serial.RtsEnable = false;
                _serial.Open();

                _serial.Write(new byte[] { 0xff }, 0, 1);
                _serial.BaseStream.Flush();

                SendEmptyBuffer(20);

                _serial.Write(new byte[] { 0x80 }, 0, 1);
                _serial.BaseStream.Flush();

                while (!Console.KeyAvailable)
                {
                    var request = _serial.ReadByte();

                    switch (request)
                    {
                        case 0x00:
                            SendBuffer();
                            break;

                        case (byte)'S':  // S -> P
                            _serial.ReadByte();
                            break;

                        default:
                            Console.WriteLine("Receive: {0:x2}", request);
                            break;
                    }
                }

                _serial.Write(new byte[] { 0x81 }, 0, 1);
                _serial.BaseStream.Flush();
            }
        }
    }
}